Chinese premier Li Keqiang has pledged to make the country's skies blue again and "work faster" to address pollution caused by coal burning.

His words to delegates at the opening of the annual National People's Congress highlight how public discontent has made reducing smog, the most visible of China's environment problems, a priority for the leadership.

In a report to China's ceremonial legislature, Mr Li said people are "desperately hoping for" faster progress to improve air quality.

"We will make our skies blue again," he declared to almost 3,000 delegates in the Great Hall of the People in Beijing.

He said the government intends over the next year to step up work to upgrade coal-fired power plants to achieve ultra-low emissions and energy conservation, and prioritise the integration of renewable energy sources into the grid.

Environmental groups welcome the disclosure of such data because it allows the public to directly supervise the emissions of plants in their areas.

Lauri Myllyvirta of Greenpeace said the group had expected the government to announce a speeding-up of measures because air pollution is supposed to hit targets this year that were laid down in 2013. They include a 25% reduction in the density of fine particulate matter - a gauge of air pollution - in Beijing and the surrounding region from 2012 levels.

"It will require very dramatic steps to achieve those targets for this year," Mr Myllyvirta said.

He added that Greenpeace also hopes to see a measurable target for reducing wasted wind and solar power generation capacities, "because that's when different parts of the government will be really held accountable for integrating wind and solar fully into the grid".

Mr Li said the government would ramp up efforts to deal with vehicle emissions by working faster to take old vehicles off the roads and encourage the use of clean-energy cars.

He said authorities will "strictly enforce" environmental laws and regulations and that officials who do a poor job in enforcing the law or respond inadequately to worsening air quality will be held "fully accountable".

Local officials have often been lax at enforcing regulations on companies that contribute to economic growth in their areas.

Official data shows an improvement in China's air quality since 2013, when the government brought out its air pollution action plan. However, residents in cities including Beijing still regularly breathe levels of pollution several times higher than the recommended safe limit, and use apps to monitor air quality.

Mr Li also trimmed China's growth target and warned of dangers from global pressure for trade controls, as Beijing tries to build a consumer-driven economy and reduce reliance on exports and investment.

He promised more steps to cut surplus steel production that is straining trade relations with the US and Europe. He pledged equal treatment for foreign companies, apparently responding to complaints that Beijing is trying to squeeze them out of technology and other promising markets.

Mr Li's report set the growth target for the world's second-largest economy at "around 6.5% or higher, if possible".

That is down from 6.7% last year but, if achieved, would be among the strongest globally, reflecting confidence that efforts to create new industries are gaining traction.

Mr Li called for attention to the risks of China's surging debt levels, which economists see as a rising threat to growth. He announced no major initiatives, but that was widely expected as the ruling Communist Party tries to avoid shocks ahead of a congress late this year at which President Xi Jinping is due to be given a second five-year term as leader.

Chinese leaders have publicly defended free trade in response to President Donald Trump's promises to raise duties on Chinese goods, although Beijing's trading partners complain that it is is the most closed major economy.

China "may be adversely affected" if Mr Trump goes ahead with "tough policies", but the impact should be limited, said economist Song Lifang at Renmin University in Beijing.

"With China's domestic economy still in the phase of transformation, the tasks for China's economic growth are arduous but with great potential."